1. Field of the Invention
The present invention relates to a network relay apparatus and method for relaying multiple networks and more particularly to a network relay apparatus and method for controlling different network apparatuses mutually.
2. Description of the Related Art
In recent years, with prevailing of various kinds of digital apparatuses, network communication technology among the digital apparatuses has been demanded to raise its reliability and diversify its function. As one of communication technologies for a network constituted of such multiple audio visual apparatuses, IEEE1394 standard is available. In a network constructed of the IEEE1394 serial bus, respective audio visual apparatuses use allocated address spaces each having fixed 64 bits specified according to IEEE1212CSR (control and status register architecture). Further, the IEEE1394 defines read transaction, write transaction and lock transaction requested by the IEEE1212CSR.
Further, as a standard used for realizing control state and controlled state among the respective AV apparatuses, AV/C digital interface command set (hereinafter referred to as AV/C command) specified by 1394TA (1394 trade association) is available. The AV/C command realizes control and state acquisition of other apparatus through write transaction using function control protocol (FCP) specified by the IEC61883. Under the AV/C command standard, AV/C unit model and AV/C sub-unit model are defined as a model which logically expresses the function of the AV apparatus. The AV/C sub-unit model is a model expressing the function of a device loaded in an AV apparatus, and, for example, tuner unit, monitor sub-unit, VTR sub-unit, disc sub-unit and the like are defined. The AV/C unit model is a logical model expressing the AV apparatus and capable of possessing one or multiple AV/C sub-unit units. The AV/C unit and the AV/C sub-unit have a logical interface called plug as an interface with outside, respectively. By transmitting this AV/C command to the AV/C unit or the AV/C sub-unit, this AV apparatus can be controlled or its information can be obtained.
On the other hand, in order to send/receive AV stream between the apparatuses through the IEEE1394 serial bus, write and read are carried out to the plug control register (PCR) defined by the IEC61883 using read transaction and lock transaction based on connection management procedure (CMP) specified by the IEC61883, thereby establishing logical connection (hereinafter referred to as connection).
Upon communication based on such a network standard, if an apparatus existing on one network intends to access and control another apparatus existing on other network when multiple networks exist independently, data is transmitted through a bus bridge connecting between the networks. Then, to carry out such data transmission between networks, software and hardware meeting the bus bridge are necessary, so that its required system is expanded in terms of scale. Further, because the status of an apparatus on one network cannot be known directly from the other network, the apparatus on a different network cannot be controlled easily as a different apparatus on the same network.
That is, in the conventional system, if multiple independent networks exist, the status of an apparatus on one network cannot be known from the other network easily. Therefore, an apparatus existing on a different network cannot be monitored or controlled like an apparatus existing on the same network easily.